The technical field of the invention is methods for improving navigation and piloting efficiency of maritime vessels, especially of inland waterway tow boats.
In the maritime industry, many bulk goods, both dry and liquid, are transported on the inland and intra-coastal waterway systems in unpowered barges. The inland waterway system in the United States includes major rivers, such as the Mississippi, Ohio and Missouri Rivers. Intra-coastal waterways include bays and sounds along the East Coast of the United States, as well as various canals connecting those bodies of water.
Unpowered barges are typically pushed along the waterways by a towboat. A towboat has sufficient power to push at least 9-15 fully loaded barges. When moving along a waterway, the barges are secured together in a rectangular grid, called a barge tow. Typical barge tows may be 2 or 3 barges wide by 3 to 5 barges long. The width of the tow is generally limited by the locks along the waterway through which the barge tow will have to pass. On the Mississippi River downstream of St. Louis, Mo., where no locks are present, barge tows may comprise as many as 40-50 barges. The larger towboats needed to push these larger barge tows are referred to in the industry as line boats.
For moving a barge tow along a waterway, the tow boat is secured to the aft row of barges of the barge tow. The towboat is typically secured in a manner preventing any relative rotation of the tow boat with respect to the barge tow. When a tow boat maneuvers by rotating its rudder, the combination barge tow/tow boat turn as a single unit. Because of the large mass of a fully-loaded barge tow, a towboat must impart relatively large amounts of energy to overcome the momentum of the barge tow, either in initially making way, in turning or changing course, or in coming to a stop. In maneuvering along the bends and meanders of the inland waterways, the course of the barge tow must change frequently. To change the course of a barge tow, the towboat must apply a turning moment well before the actual bend in a river, and apply a reverse turning moment well before the completion of the turn, to keep the barge tow within the river channel. An inexperienced helmsman will often under- or over-steer in the river bends, necessitating repeated corrections to bring the combination barge tow/tow boat on course within the river channel. The repeated starboard and port corrections by a helmsman of the barge tow towboat combination will be apparent in the wake of the towboat, which will appear as a series of lateral undulations stretching back from the stern of the towboat. These repeated corrections represent wasted fuel and wasted time for the towboat.
In addition to receiving GPS satellite transmissions and trilaterating its current position, GPS receivers often contain programming which interpolates a series of geographical positions to determine the direction and speed of a moving positional sensor by use of regression analysis on a series of recent positional fixes.
More advanced GPS receivers may as well include an integral electronic compass. Such devices incorporate integrated circuits having a magneto-resistive sensor. This allows a determination of which way the GPS receiver is terrestrially aligned, i.e., its heading with respect to either true or magnetic north, regardless of which direction the GPS receiver determines it is moving. Further, regression analysis on a series of subsequent headings can determine the rate at which a positional device is turning or rotating, even if remaining at a fixed geographical location.
GPS receivers may display their location and other derived information on an integral screen or display. They may also transmit the data either by cable or by radio or other wireless means, to another electronic device, such as a computer. In a computer, further numerical analysis may be performed on the data transmitted by the positional device.
The prior art has various examples of methods of automatic controls of marine vessels to improve the maneuvering of the vessels over that of manual helm control. For example, U.S. Pat. No. 5,034,895, entitled “Enhanced Performance Bias Integrator for Marine Automatic Pilot System,” issued to Johnson et al. on Jul. 23, 1991, teaches a rudder order bias integrator of a marine autopilot for removing offsets by calculating a correction to any heading error bias resulting from wind, seaway effects or hull, propulsion or cargo assymetries (col. 1, II. 30-39). However, the rudder order bias integrator disengages during a turning maneuver of the ship, though it automatically reengages at the end of the turning maneuver (col. 2, II. 22-23). Other references in the prior art, including U.S. Pat. No. 4,074,648, issued Feb. 21, 1978 to Reid and Wesner and U.S. Pat. No. 4,692,868, issued Sep. 8, 1987 to Wesner. These also teach means of correcting the heading of a marine vessel. However, they likewise do not function during an intended heading change of the vessel.